The present invention relates generally to antennas, and more particularly to antennas used with wireless communicators.
Radiotelephones generally refer to communications terminals which provide a wireless communications link to one or more other communications terminals. Radiotelephones may be used in a variety of different applications, including cellular telephone, land-mobile (e.g., police and fire departments), and satellite communications systems. Radiotelephones typically include an antenna for transmitting and/or receiving wireless communications signals.
Radiotelephones and other wireless communicators are undergoing miniaturization. Indeed, many contemporary radiotelephones are less than 11 centimeters in length. As a result, there is increasing interest in small antennas that can be utilized as internally-mounted antennas for radiotelephones.
Inverted-F antennas may be well suited for use within the confines of radiotelephones, particularly radiotelephones undergoing miniaturization. As is well known to those having skill in the art, conventional inverted-F antennas include a conductive element that is maintained in spaced apart relationship with a ground plane. Exemplary inverted-F antennas are described in U.S. Pat. Nos. 5,684,492 and 5,434,579 which are incorporated herein by reference in their entirety.
In addition, it may be desirable for radiotelephones to operate within multiple frequency bands in order to utilize more than one communications system. For example, GSM (Global System for Mobile communication) is a digital mobile telephone system that typically operates at a low frequency band, such as between 880 MHz and 960 MHz. DCS (Digital Communications System) is a digital mobile telephone system that typically operates at high frequency bands, such as between 1710 MHz and 1880 MHz. The frequency bands allocated in North America are 824-894 MHz for Advanced Mobile Phone Service (AMPS) and 1850-1990 MHz for Personal Communication Services (PCS). Accordingly, internal antennas, such as inverted-F antennas are being developed for operation within multiple frequency bands.
There is also interest in utilizing retractable antennas that-can be extended from communications devices, such as radiotelephones. Retractable antennas may enhance signal transmission and reception, particularly in communications devices utilizing code-division multiple access (CDMA) wireless telephone transmission technologies. Some conventional wireless communicators, such as radiotelephones, utilize a one-quarter wavelength whip antenna in combination with a one-quarter wavelength stub antenna. When extended, the whip antenna combines with the stub antenna to provide one-half wavelength performance. When the whip antenna is retracted, the stub antenna provides one-quarter wavelength performance.
Unfortunately, communications devices that utilize retractable/internal antenna combinations and retractable/stub antenna combinations may require complex switching schemes which, in turn, may increase manufacturing costs and may present reliability concerns. Moreover, dual-band retractable antennas having one-half wavelength performance may be unavailable without impedance matching circuitry.
In view of the above discussion, antenna systems for use within wireless communicators, such as radiotelephones, according to embodiments of the present invention, include a first antenna configured to be internally mounted within a wireless communicator and a retractable, second antenna that electrically couples with the first, internal antenna when the retractable, second antenna is extended. The internal, first antenna may be resonant within one or more frequency bands and the retractable, second antenna is configured to couple with the internal, first antenna so as to enhance one or more of the resonant frequency bands. When in the extended position, the retractable, second antenna may be parasitically coupled with the internal, first antenna, or may be directly connected to the internal, first antenna.
According to embodiments of the present invention, the internal, first antenna is an inverted-F antenna. The retractable, second antenna, according to embodiments of the present invention, includes a one-quarter wavelength whip portion with a one-quarter wavelength helix antenna at a free end thereof. The helix antenna is physically connected to the whip portion, but may be electrically connected to, coupled to, or isolated from the chip antenna.
Antenna systems according to the present invention may be particularly well suited for use within wireless communicators, such as radiotelephones, wherein space limitations may limit the performance of internally mounted antennas. The combination of a retractable, second antenna with an internal inverted-F antenna according to embodiments of the present invention may enhance the performance of the internal inverted-F antenna when the retractable, second antenna is extended. Furthermore, the combination of internal and retractable antennas according to embodiments of the present invention may not require impedance matching networks, which may save internal radiotelephone space and which may lead to manufacturing cost savings.